This application is a continuation-in-part of Application Ser. No. 57,564 filed June 15, 1987 which is a continuation-part of Application Ser. No. 890,712, filed July 30, 1986 all now abandoned.
Thermoplastic multi-block copolyester elastomers have gained acceptance in many fields because of their outstanding physical properties which are unique in relation to other thermoplastic polymers. However, copolyester elastomers are flammable and this limits their usefulness for preparing electrical parts, wire coverings for telecommunications, optical fiber outer jacketing and other applications where fire retardant materials are needed.
Numerous halogenated organic compounds either alone or in combination with antimony trioxide have been tested and recommended for use in polyester homopolymers or random copolyesters, as have various inorganic additives. Because of the relatively high flammability of multi-block copolyesters, the ease with which such copolyesters undergo degradation during melt processing, and the difficulty of retaining a useful amount of flexibility in the multi-block copolyesters in the presence of significant amounts of added materials, there still is a need for fully acceptable fire resistant multi-block copolyester compositions that are substantially nondripping when burned and, most importantly, the copolyester compositions should generate a minimum amount of smoke and form a large amount of char when burned. Also, the thermoplastic compositions must be extrudable and retain a good combination of physical properties. The present invention provides flame resistant multi-block copolyester compositions which do not exhibit enhanced degradation. The compositions of this invention are low smoke generating and high char forming; do not drip when burned; and have V-O ratings for flammability according to the UL-94 Vertical Burn Test.
Recently, substantially nondripping flame resistant multi-block copolyester compositions have been developed by incorporating in the copolyester a combination of a flame retardant to resist burning and a drip suppressant such as fumed colloidal silica or an organophilic clay. Such flame resistant copolyester compositions that are substantially nondripping are described in U.S. Pat. No. 4,521,557 to McKenna dated June 4, 1985 and U.S. Pat. No. 4,582,866 to Shain dated April 16, 1986, both patents assigned to E. I. du Pont de Nemours and Company. These flame resistant copolyester compositions referred to above are quite useful especially for coverings on optical fibers and wire since they are substantially nondripping when burned. However, these flame resistant nondripping multi-block copolyester compositions when burned generate considerable amounts of smoke and, unfortunately, only small amounts of char. For many uses, for example plenum cable covering, the compositions should not only be flame resistant but the compositions should be as smokeless as possible. Smoke, of course, presents a serious hazard during a fire and causes secondary damage over a large area involved in the fire. Also, it is important that the compositions form a high percentage of char when burned. High char formation is beneficial because char has enough integrity to remain in place, for example, on a bundle of wires, while the polymer is burning and the char functions during the fire as an insulator. The char keeps some of the heat of the external fire away from the wire bundle, minimizing its contribution to the flame and maximizing the length of time during which the wires perform their normal function. Many compositions have been rejected by manufacturers because of the large amounts of smoke they generate and the small amount of char formation made by the polymers when burned.
The present invention that is directed to a novel copolyester composition is especially useful for covering bundles of insulated telecommunication wires, e.g., optical fibers, metal wires, etc., with a flame-protective jacketing material. The copolyester compositions of the present invention are not only flame resistant and substantially nondripping but, in addition, most importantly, these compositions burn without generating much smoke and they form large amounts of char. The copolyester compositions of this invention can be characterized as low smoke generating and high char forming, primarily due to the addition of relatively small amounts of char-forming additives, and can do so without intumescing into a ceramic barrier. The copolyesters used in the flame retardant compositions have a melt flow rate of at least 0.4 g/10 minutes, usually 0.9 g/10 minutes, at 190.degree. C. which makes the compositions readily processible. Also, to substantially improve the physical properties of the composition of this invention coupling agents, when added, have unexpectedly substantially increased the tensile strength of the compositions.